Use boringssl prf for tls1.2

boring-sys-additions/src/lib.rs

@@ -0,0 +1,22 @@
+use std::ffi;
+
+extern "C" {
+    /// Calculates `out_len` bytes of the TLS PDF, using `digest`, and
+    /// writes them to `out`. It returns one on success and zero on error.
+    ///
+    /// This isn't part of the public headers in `BoringSSL` but it is exported
+    /// in `crypto/fipsmodule/tls/internal.h` :)
+    pub fn CRYPTO_tls1_prf(
+        digest: *const boring_sys::EVP_MD,
+        out: *mut u8,
+        out_len: usize,
+        secret: *const u8,
+        secret_len: usize,
+        label: *const u8,
+        label_len: usize,
+        seed1: *const u8,
+        seed1_len: usize,
+        seed2: *const u8,
+        seed2_len: usize,
+    ) -> ffi::c_int;
+}